The present invention relates to communication networks using i.a. ATM-(Asynchronous Transfer Mode) connections for data transmission, particularly ATM-connections adapted for transmission of, e.g., IP-packets.
The ATM (Asynchronous Transfer Mode)-technology has received a lot of attention as a major transport technology. ATM intends to combine the advantages of the basic switching technologies circuit-switching and packet-switching. Circuit-switched networks, on the one hand, are rather simple while being capable to provide high bit rates and guaranteed small delay times. Packet-switched networks, on the other hand, provide the greater flexibility and, above all, efficient multiplexing facilities. Thus, ATM-based communication networks can be characterised as high-speed switching systems offering large bit pipes, allowing statistical multiplexing while reducing the overall bandwidth requirements. The fundamental strategy behind ATM is to split information that is to be transmitted into small units, so called cells, with a fixed cell size of 53 bytes divided into a 5 byte header portion and a 48 byte payload field. FIG. 1 presents the ATM reference model for a brief description of data transmission in ATM-networks. Said model consists of four protocol levels: The lowest level is the physical level 11. As ATM is designed to be independent of a specific transmission medium it is possible to use wired or wireless connections or even package the ATM-cells inside the payload of other carrier systems. Objects of the ATM-layer 12 are, i.a., to build ATM-cells and to establish and release virtual connections that are intended to transport said cells. On top of said ATM-layer 12, an ATM adaptation layer (AAL) has been defined as a kind of interface towards protocols that do not operate on a cell basis. Said adaptation layer is divided into two sublayers: The Convergence Sublayer 13b contains an application specific subpart and a common part that is responsible, e.g., to break down data streams or frames messages into smaller units of 44 to 48 bytes and vice versa. The Segmentation Reassembly Sublayer 13a is mainly used to forward and receive cell payloads to and from the ATM-layer 12. There have been defined several alternative variants of AAL, because said adaptation layer is intended to adapt the ATM-protocol to protocols of the application layer 15 that require various service requirements and use various traffic classes, e.g. with respect to delay conditions, bit rates, and the kind of connection that shall be applied. The present invention mainly focuses on AAL5.
Yet another protocol structure is represented by the TCP/IP reference model as shown in FIG. 2. Said model refers to a packet-switched network that applies on the network layer 22 the Internet protocol (IP), which provides a connectionless, unreliable communication between two arbitrary hosts in an internet consisting of a plurality of interconnected subnetworks. On the transport layer 23 either TCP or UDP is implemented for providing a reliable or unreliable communication service, respectively, to the upper layer protocols that are used on the application layer 24. With respect to the lowest layer 21, the IP-protocol does notxe2x80x94and shall notxe2x80x94rely on a specific communication protocol, e.g. between two adjacent hosts, as it must be able to forward IP-packets throughout a plurality of interconnected networks using a variety of different data link layer protocols. Thus, it is possible to apply, e.g., the ATM-protocol structure as described above as a kind of underlying transport protocol for IP-packets in the meaning of the TCP/IP reference model.
Third generation communication systems, e.g. the Universal Mobile Telecommunication System (UMTS) as defined by the European Telecommunications Standards Institute (ETSI) have been developed with regard to certain key factors, e.g. multimedia capability or bandwidth on demand, in order to provide a wide and flexible range of services to their user equipments. UMTS supports a modularly architecture concept consisting of two major parts: The UMTS core network is responsible for providing telecommunication services, i.a. call and subscriber data management, and for providing access to other communication networks, e.g. PSTN or Internet. The UMTS Radio Access Network is mainly responsible for managing the radio functionality for connections between core network and the user equipments. This UMTS Terrestrial Radio Access Network (UTRAN) consists of at least one Radio Network Controller (RNC) and a plurality of Radio Base Stations (RBS). Transport of user data and control signalling data between said Radio Network Controllers and/or the various Radio Base Station nodes is done by means of connections using an ATM-based protocol structure. Additionally, a management system must be implemented and capable to access the network nodes, e.g. via an Ethernet connection to at least one node in the Radio Access Network. Examples of management activities are configuration of network nodes, remote downloading of software, and performance measurements. These management systems often use protocols based on the Internet Protocol (IP), e.g. File Transfer Protocol (FTP), Hypertext Transfer Protocol (HTTP), Telnet, or Simple Network Management Protocol (SNMP), and can be located either centrally in a Radio Access Network Operations System (RANOS) in the UMTS Radio Access network or in a thin client terminal that is connected locally to a Radio Network Controller or a Radio Base Station. Also the Network Time Protocol, which is used for synchronisation of the real-time clocks in UTRAN nodes, is based on the Internet Protocol. Therefore, an IP-network is to be built between the network nodes and the management system by using the ATM infrastructure of the UMTS Radio Access Network. Accordingly, the present invention intends to solve the problem of an interworking between management system and Radio Access Network that is done such that IP-based management messages can be transmitted via the ATM-based access network and such that the management communication with a node shall be maintained as long as there exist a physical link that can carry ATM-connections to this node.
The topology of an IP-based management network in the UMTS Radio Access Network can be modelled as a plurality of nodes with an implemented IP-functionality that are interconnected by means of ATM-based point-to-point connections to other nodes and that are accessible for a management system. The management system can thus access the management functions in said nodes by means of the IP-addresses that are assigned to these nodes. As each such IP-node comprises a routing functionality, IP-packets can be forwarded to a destination node (RNC or RBS) via several intermediate nodes by using said ATM-based point-to-point connections and/or via, e.g., Ethernet between said nodes and the management system. One known solution for transportation of IP-packets over ATM-based point-to-point connections is the usage of the ATM Adaptation Layer 5 (AAL5) protocol and encapsulation of IP-packets as specified in the Request for Comment (RFC) 2225 (xe2x80x9cClassical IP and ARP over ATMxe2x80x9d). Nodes in the UMTS Radio Access Network are always interconnected by at least two physical links with ATM-capability and the IP-protocol uses ATM as an underlying packet transport protocol. For transport of IP-packets, these ATM-connections are designed as Permanent Virtual Channel (PVC-) connections that are either pre-configured for said nodes or established by the management system. Each of these point-to-point connections is modelled as an IP-subnetwork with one IP-address defined for each end of the link. Routing of IP-packets in an IP-node is done on the IP-level by means of selecting an appropriate IP-subnetwork, i.e. selecting one of the available ATM-connections to a subsequent node, and applying said selected subnetwork address as the forwarding address by the routing procedure.
The solution as described above implies certain limitations: The number of nodes, e.g., in an UMTS Radio Access Network, and thus the number of ATM-connections, might become considerably large. The number of IP-subnetworks for each of said ATM-connections will increase accordingly. Therefore, it becomes apparent that a growing network implies an increasing number of IP-subnetworks that must be administered. It is another limitation of said solution that an ATM-connection that becomes inoperative causes that the corresponding IP-link, which applies said connection, will also become inoperative. This will be detected by the IP routing protocol in the two affected nodes that were interconnected by said inoperative ATM-connection and is interpreted as a change in the topology of the IP-network.
The measure taken will then be that said change is announced to the other nodes in the network and the routing protocol in each node must recalculate its routing table in order to circumvent the IP-subnetwork with the inoperative connection by reselecting a redundant IP-subnetwork between the two affected nodes and switching over data traffic to said IP-subnetwork. This causes an additional network load due to the fact that the topology change must be distributed to the nodes of at least parts of the network. Also, the switch over to the redundant IP-subnetwork cannot take place immediately since the nodes will have to recalculate their routing tables.
In general terms, the present invention relates to a plurality of interconnected nodes, at least parts of which forming a first communication network applying a first communication protocol and at least parts of which forming a second communication network applying a second, e.g. packet-based, communication protocol, whereby said second communication protocol uses said first communication protocol as an underlying data transport protocol.
It is a first object of the present invention to achieve a second communication network consisting of a number of subnetworks, and thus assigned addresses, that is reduced in such a way that the reliability of said subnetworks is enhanced.
It is another object of the present invention to achieve a second communication network that allows data transfer via links between nodes, said links consisting of several point-to-point connections, such that the management of said links according to the second communication protocol is independent of the management of said point-to-point connections according to the first communication protocol.
It is still another object of the present invention to achieve a communication network having a reduced amount of network administration traffic due to topology changes in the second communication network, which are caused by topology changes, e.g. due to connection failures, in the first communication network.
It is a particular object of the present invention to achieve a network node using IP as the first communication protocol and using ATM as the second communication protocols, said node comprising a function block that allows transmission and reception of IP-packets via one single access point and that can access one or more ATM-connections for transmission or reception of IP-packets.
It is yet another object of the present invention to achieve a method for efficient transmission and routing of IP-packets in an ATM-based communication network.
Briefly, these and other objects of the present invention are accomplished by the method and arrangement according to the present invention comprising a link function block that is implemented in a number of nodes in a communication network including means for selecting an operative point-to-point connection, e.g. an ATM-connections, that is applied as part of a link for data transmission and/or reception, e.g. by means of IP-packets, between two arbitrary nodes. Said function block also includes means for monitoring the operability of assigned point-to-point connections and means for reselecting a redundant connection if one of said selected connections is detected to be inoperative.
As a first advantage, the present invention allows a plurality of nodes to be interconnected by a reduced number of subnetworks.
It is thus an advantage of the present invention that network addressing and administration can be done in a more efficient way even for an increasing number of network nodes.
It is another advantage that an end-to-end protocol will experience only infrequent changes in the network topology due to an enhanced reliability of the subnetworks.
It is thus another advantage of the present invention that less network administration information need to be broadcasted between the nodes in the communication network.
It is still an advantage of the present invention that routing in the network can be performed in a more efficient way. Said efficiency implies shorter time delays due to the reduced number of subnetworks and due to infrequent changes in the network topology and less network load due to a reduced broadcast of network administration information.
It is in particular an advantage of the present invention that transmission and routing of IP-packets over ATM-connections is done in a more efficient and reliable way.
Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings and claims.